1. Field of the Invention
The invention relates generally to measurement of the hydraulic conductivity of porous materials and particularly to a method and apparatus for directly measuring hydraulic conductivity of porous materials at various degrees of saturation without the need for measuring fluid discharge and piezometric head gradient.
2. Background of the Invention
Existing methodology and apparatus for measuring the hydraulic conductivity of porous materials exhibit characteristics which limit the accuracy of hydraulic conductivity measurements thereby produced. Prior apparatus, generally known as permeameters, are typically configured such that dissolved gases which are contained in fluids supplied to a sample often come out of solution and affect flow within the sample. Similar errors can be introduced in prior permeameters by temperature variations which affect viscosity, these thermal variations being difficult to control with prior apparatus. Further, small discharges and gradients are difficult to measure and, in prior apparatus, must be measured in order to produce usable results. Errors are also introduced in prior apparatus by factors as simple as evaporation losses from the reservoirs which supply fluid to the samples.
As will be discussed in more detail hereinafter, and immediately prior to a detailed description of the preferred embodiments of the invention, present methods for measuring hydraulic conductivity of unsaturated and saturated materials depend on the measurement of fluid discharges and piezometric head gradients. In these prior procedures, a fluid is typically allowed to pass through a sample of material on the way from a first reservoir to a second reservoir. Examples of such prior art permeameters include the constant head permeameter and the variable head permeameter which are well known in the art. For unsaturated materials, a permeameter must be operated at air pressures less than the air entry pressure of the porous plate materials forming the interfaces between the sample and the fluid reservoirs.
Prior permeameters and similar apparatus disclosed in issued United States patents include U.S. Pat. No. 3,435,663 to De Lamballerie which discloses apparatus for determining the permeability of a ground sample which is placed in a chamber with drilling mud with heat and pressure being applied to the sample to force the mud through the sample. Particular attention is given in the apparatus of De Lamballerie for compensating for temperature conditions and differential pressure conditions.
U.S. Pat. No. 3,683,674 to Roy discloses a porosimeter for measuring the size-volume distribution of porosity of a porous member. The apparatus of Roy includes a rotating sample chamber. However, the device of Roy is not capable of making the same measurements as that of the present permeameter and Roy does not disclose the particular apparatus of the present invention.
Russian Pat. No. 787,951 also describes a porosity tester which utilizes a rotating drum. However, in a manner similar to that described above relative to Roy, the Russian patent does not disclose apparatus capable of performing the permeability or hydraulic conductivity measurements to which the present invention is addressed.
Accordingly, the present invention allows the measurement of hydraulic conductivity without the inaccuracies and measurement problems associated with the prior art. By measurement of hydraulic conductivity from the motion of fluid which is fully contained within a porous sample, the present invention eliminates measurement difficulties associated with both dissolved gases and evaporation and also minimizes thermal affects by allowing better temperature control within the test system. Since it is not necessary to measure discharge or piezometric head gradients in the practice of the present invention, errors inherent in such measurements with existing technology are obviated, the present invention requiring only measurements which can be made in a precise manner. Further, under unsaturated conditions, measurement problems inherent in the prior art and which are associated with the use of porous plates and the like are eliminated. The present invention thus exhibits substantial advantages over the prior art.